Three filament bulb



May 24, 1932. R, N, FALGE 1,859,661

THREEFILAMENT BULB Filed Sept. 1. 1928 Patented May 24, 1932 UNITED STATES PATENT OFFICE ROBERT N. FALGE, 013 DETROIT, MICHIGAN, ASSIGNOB TO GENERAL MOTORS RESEARCH CORPORATION, OF DETROIT, MICHIGAN, A CORPORATION OF DELAWARE THREE FILAIVIEN T BULB Application filed. September 1, 1928.

This invention relates to incandescent lamps, such as are commonly used in automobile headlights.

Heretofore when the filament of such a lamp became broken, the car has usually been driven along with but one headlamp in service so that it constituted a menace to other drivers because of their inability to gauge its position on the road. To avoid this difficulty, T have devised a lamp with an auxiliary filament which operates when the main filament is broken to provide a marker in the headlight, which indicates the position of the car. If desired, the auxiliary filament may be of suflicient candle power to provide more or less illumination of the road. Preferably, however, the resistance of the auxiliary filament is great so that it gives but little light and it is also designed so that its life is very, long, insuring that it will outlast the main filament and will consequently alwaysbe effective as a safety device.

In its simplest form, the auxiliary filament may simply be connected in parallel with a major filament, and in the case of two filament lamps, each filament may be thus equipped. However, in the latter case for cheapness and simplicity, I prefer to arrange one auxiliary filament so that it will serve as a marker in case either of the major filaments becomes broken. This maybe accomplished in a simple manner in the ordinary two filament lamp by connecting the auxiliary filament across the independent leads which supply the major filaments with current. These filaments are usually provided with a common return lead so that the edect of the auxiliary filament is to provide a path for the current in parallel with the, filament which is energized. This path includes the auxiliary filament and the major filament which is not in use. The resistance of this path is so great that but a small amount of current flows but the current is nevertheless suflicient to cause the auxiliary filament'to glow. This it will do all the time that the major filament is in service and should that filament become broken, the glow from the auxiliary filament will still give sufficient illumination to the lamp to make it serve as a marker,.with the Serial No. 303,443.

advantages above pointed out. The candle power of the auxiliary filament is preferably not sulficient to have any objectionable efiect on the illumination from the major filament.

Obvious, with the auxiliary filament located as described, the same action will take place when the second filament is energized.

In the drawings:

Figure 1 indicates my improved lamp in use in a reflector of a two beam automobile headlight. In this view the lamp is slightly tilted out of its normal position in the refiector so as to better show the filament construction.

Figure 2 is an enlarged fragmentary view of the lamp shown in Figure 1.

Figure 3 is an end view of Figure 2.

Figure 4 shows the circuit arrangement of the lamp of Figure 1.

Figure 5 shows a modified filament arrangement.

Figure 6 shows the circuit arrangement of the form shown in Figure 5.

in Figure 1, T have shown at 10 an incandescent lamp having the filaments arranged in accordance with the preferred form of my invention. The lamp is provided with major filaments 12 and 14, supplied with current through independent leads 16 and 18 respectively. A common return lead 20 completes the circuit. This circuit is best shown in Figure 4. 22 indicates my auxiliary filament which is connected across the leads 16 and 18. This filament is preferably of quite high resistance; thus, while the major filaments 12 and 14 are each preferably.

of 21 candle power, the minor filament 22 may be of but two candle power. While this is the preferred ratio of resistances of the filaments, it is obvious that it is within the range of engineering expedients to vary these resistances as may be deemed most desirable. Thus in some instances, it may be even expedient to make the auxiliary filament of equal or less resistance than the major filaments.

I have illustrated my improved bulb as mounted in a reflector 24 having a top portion 26 and a bottom portion 28, bent downwardly from true parabolic form so that till lead 20. The combined resistance of the leads 22 and 14 is preferably such as to allow the passage of sufficient current to cause the filament 22 to glow slightly providing the desired two candle power. The heating effect of the current upon the filament 14 is insuflicient to cause it to glow so that the passage of current has practically no efiect on its life. Exactly the same operation results when the filament 14 is lighted, some of the current supplied by the lead 18 then passing through filaments 22 and 12 in series to the return lead 20.

The auxiliary filament may be added to the conventional construction at very slight cost and provides a safety feature of considerable value. It may also be designed to give more or less illumination as may be desired. When designed for low candle power, extremely long life is assured so that there is no possibility of its becoming broken or burned out before the major filaments.

In the modification shown in Figures 5 and 6, the auxiliary filaments 30 and 32 are connected across the major filaments 12 and 14 respectively. This is a more expensive construction since two auxiliary filaments are required. i

I claim:

1. An incandescent lamp for automobile headlamps provided with concentrated filaments having a common lead and insulated leads, and a long life concentrated auxiliary filament connecting said insulated leads.

/ 2. An incandescent lamp provided'with a plurality of filaments, insulated leads connected to one end of each of said filaments so that each may be separately, supplied with current, a common return lead connected to the other ends of said filaments, an auxiliary filament connecting said filaments adiacent their first named ends. said auxiliary filament serving as a marker in case of breakage of either of the other filaments. I

3. An incandescent lamp provided with a plurality of filaments, insulated leads connected to one end of each of said filaments so that each may be separately supplied with current, and an auxiliary filament electrically connecting said filaments at points removedirom the connection of said filaments to the common return lead so that when one filament is lightedthe auxiliary filament and at least a portion of the other filament will either of the other filaments.

4. An incandescent lamp provided with a plurality of main filaments of high candle power, insulated leads connected to one end of each of said filaments so that each may be separately supplied with current, an insulated return lead connected to the other ends of said filaments, and an auxiliary filament of low candle power electrically connecting said main filaments at points removed from the connection of said main filaments with the return lead, said auxiliary filalnentbeingfaintlyilluminated when either of the other filaments is lighted, by passage of current through it and at least a portion of the other of the main filaments inseries, said auxiliary filament thereby serving as a marker should the lighted filament break.

5. An incandescent lamp having a glass envelope and a base provided with a plurality of spaced insulated contacts, a plurality of supports extending from the base, each arranged in series with one of said contacts, one of said supports being provided with a forked free end extending Within the envelope, independent filaments of high candle power, each extending between one of the ends of the fork and another of saidsupports and an auxiliary filament connecting said independent supports.

' In testimony whereof I affix my signature.

ROBERT N. "FALGE. 

